f - avoid string copy when possible

Author: jkczyz

lightning/src/offers/parse.rs

@@ -25,15 +25,22 @@ pub(crate) trait Bech32Encode: AsRef<[u8]> + TryFrom<Vec<u8>, Error=ParseError>
 	/// Parses a bech32-encoded message into a TLV stream.
 	fn from_bech32_str(s: &str) -> Result<Self, ParseError> {
 		// Offer encoding may be split by '+' followed by optional whitespace.
-		for chunk in s.split('+') {
-			let chunk = chunk.trim_start();
-			if chunk.is_empty() || chunk.contains(char::is_whitespace) {
-				return Err(ParseError::InvalidContinuation);
-			}
-		}
+		let encoded = match s.split('+').skip(1).next() {
+			Some(_) => {
+				for chunk in s.split('+') {
+					let chunk = chunk.trim_start();
+					if chunk.is_empty() || chunk.contains(char::is_whitespace) {
+						return Err(ParseError::InvalidContinuation);
+					}
+				}
+
+				let s = s.chars().filter(|c| *c != '+' && !c.is_whitespace()).collect::<String>();
+				Bech32String::Owned(s)
+			},
+			None => Bech32String::Borrowed(s),
+		};
 
-		let s = s.chars().filter(|c| *c != '+' && !c.is_whitespace()).collect::<String>();
-		let (hrp, data) = bech32::decode_without_checksum(&s)?;
+		let (hrp, data) = bech32::decode_without_checksum(encoded.as_ref())?;
 
 		if hrp != Self::BECH32_HRP {
 			return Err(ParseError::InvalidBech32Hrp);
@@ -52,6 +59,21 @@ pub(crate) trait Bech32Encode: AsRef<[u8]> + TryFrom<Vec<u8>, Error=ParseError>
 	}
 }
 
+// Used to avoid copying a bech32 string not containing the continuation character (+).
+enum Bech32String<'a> {
+	Borrowed(&'a str),
+	Owned(String),
+}
+
+impl<'a> AsRef<str> for Bech32String<'a> {
+	fn as_ref(&self) -> &str {
+		match self {
+			Bech32String::Borrowed(s) => s,
+			Bech32String::Owned(s) => s,
+		}
+	}
+}
+
 /// Error when parsing a bech32 encoded message using [`str::parse`].
 #[derive(Debug, PartialEq)]
 pub enum ParseError {